The US government is going after drug companies, but only one group is making headway

The investigation targets Valeant Pharmaceuticals and Turing Pharmaceuticals, two of the biggest offenders of price hikes on older drugs.

Over in the House of Representatives, Democrats have also been hot on the tail of pharmaceutical companies that have jacked up the prices of some of their drugs, though they've making less headway than their Senate bipartisan counterparts. The Senate's Special Committee on Aging will hold its hearing on drug prices on Dec. 9.

In a letter sent Wednesday to Oversight and Government Reform Committee chairman US Rep. Jason Chaffetz (R-UT), committee Democrats called on him to hold a hearing on Valeant and Turing later this month.

The committee's ranking member, Rep. Elijah Cummings (D-MD), along with Democratic presidential candidate Sen. Bernie Sanders (I-VT) have been putting pressure on pharmaceutical companies to disclose more information about how they set prices.

In September, the pair sent a letter to Turing Pharmaceuticals CEO Martin Shkreli after he jacked up the price of Daraprim, a drug used to treat malaria and parasitic infections in patients with weakened immune systems, from $13.50 to $750 per pill.

Sanders and Cummings also sent a similar letter to Valeant back in August, asking for more details about how they priced two heart drugs, Isuprel and Nitropress. Valeant's Senior Vice President of Investor Relations Laurie Little responded on Sept. 3, essentially shutting the two down. "The specific documents and information referenced in your letter are highly proprietary and confidential," wrote Little.

More recently, Turing has also refused Cummings and Sanders' request for more information on its drug pricing. In a letter dated Oct. 30, Turing Chief Commercial Officer Nancy Retzlaff wrote that under the advice of legal counsel, Turing was "unable to provide certain numbers and data related to proprietary information." She added that Turing has only owned Daraprim for less than three months, which hasn't been enough time to collect the data requested.

All in all, the attempts of Sanders and Cummings' fellow Oversight Democrats have largely been ignored by Turing and Valeant, and also by Chaffetz, who ultimately sets the Oversight Committee's schedule.

"Over the past year, Democrats have asked you repeatedly to take action on this critical issue, but you have refused every request," the Oversight Democrats wrote to Chaffetz. "You have not signed one letter seeking documents from a drug company, and you have not held a single hearing to address this problem."

The Oversight Committee meeting, if scheduled, could lead to subpoenas for Turing and Valeant to produce more information about drug pricing.

Here's the response Turing Pharmaceuticals sent Business Insider in regards to the Senate Committee's letter:

"We are reviewing the Committee's request and, as we have and continue to do with similar congressional inquiries, we look forward to having an open and honest dialogue about drug pricing."